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Re: Choosing an attenuator
Can I suggest stick to dBm, using dBw, dBc etc will most likely confuse some people. On Fri, 15 Nov 2024 at 08:19, W0LEV via <davearea51a=[email protected]> wrote:
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Re: Choosing an attenuator
Well, the recommended maximum input power (and that even totaled from outside you viewing window) is -25 dBm.? 50-watts of power is +47 dBm.?? 50-watts = 10[log(50)] = +17 dBw??????? Adding 30 dB to get to dBm: +17 dBw + 30 dB = +47 dBm So, you need an attenuator of 72 dB of attenuation. 47 dBm?+ 25 dBm = 72 dB.? Of course, that's a lot.? I'd recommend several attenuators to get to -25 dBm from +47 dBm.? The first three will be expensive as they must be power attenuators.? The following will get you there: One 3 dB attenuator at 30-watts gets you to: Total of 3 dB attenuation gets you to 25 watts from 50 watts Another 6 dB attenuator at 30-watts gets you to: Total of 9 dB attenuation gets you to 6.25 watts Another 10 dB attenuator at 10-watts gets you to: A total of 29 dB of attenuation gets you to 0.625 watts
Now the attenuators are getting less expensive.
Another 10 dB attenuator at 2-watts gets you to A total of 39 dB of attenuation gets you to 0.0625 watts Another 30 dB attenuator at 2-watts gets you to A total of 69 dB of attenuation gets you to 0.00625 watts Another 3 dB attenuator gets you to the goal of 72 dB of attenuation and keeps the TinySA in the faithful measurement regime.? To do this in a single attenuator is unlikely and quite expensive.? Even breaking this down into two power attenuators of 35 dB each is still pretty expensive.?? Three power attenuators is a bit less expensive, but still expensive.? Think again about feeding 50-watts through 72 dB of attenuation directly to the TinySA!!!! Dave - W?LEV Now we're getting less expensive. Another 30 dB attenuator at 2-watts gets you to: 53 dB -? 30 dB = 20 dB Another 30 dB attenuator at 2-watts gets you to: 20 dB - 30 dB = -10 dB On Thu, Nov 14, 2024 at 8:21?PM Flex-tech via <Flex-tech=[email protected]> wrote:
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Dave - W?LEV |
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Choosing an attenuator
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It's Christmas,
Just got my TSA and I'm having a ball expoloring.
Q: I'd like to get an attenuator so I don't ruin this little gem.
I expect to be using this for a breadth of the RF spectrum ie. 108Mz up through 6 or more Gz.
I don't think the TSA will be exposed to more than 20-50 watts of tx power.
But what do I know. That's why I want some input from the forum.
Tks
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MDW |
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Re: Why transmitter power attenuator for TinySA?
Earlier, I wrote: "Maybe I misunderstand why anyone might want to connect the output port of an active transmitter to any port of a TinySA." |
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Re: Why transmitter power attenuator for TinySA?
Using filters when measuring a transmitter is fraught with problems. Without suitable attenuation *before* the filter the transmitter can see a very poor impedance which can have a significant effect on the measured results.
73 Jeff G8HUL ________________________________________ From: [email protected] <[email protected]> on behalf of Toni Ciscar via groups.io <aciscar@...> Sent: 13 November 2024 19:40 To: [email protected] Subject: Re: [tinysa] Why transmitter power attenuator for TinySA? As John Cunliffe said in this forum (/g/tinysa/message/9655), when measuring harmonics, you can use well defined high pass filters that suppresses the fundamental, for exemple, by >50db . This permits the measurement of harmonics that are very small without overloading the front end. You do only add 50 dBc to your meausurements. |
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Re: Why transmitter power attenuator for TinySA?
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Re: Why transmitter power attenuator for TinySA?
Just to give an idea about the dynamic range of the tinySA when measuring harmonics here a measurement of the harmonics of a 11 MHz signal
Input is at -25 dBm
All settings default
Set to MEASURE/HARMONIC with frequency set to 11 MHz and span set to 20 kHz
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The 2nd harmonic is below -75dBc and the 3rd harmonic below -83dBc
Only when you need to measure harmonics below these levels an input high pass filter may be needed.
For transmitters output measurements probably not.
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Designer of the tinySA
For more info go to |
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Re: Setup FM mobile VHF transceiver's deviation with VaraFM
Let's give people the dBm view. 5W = 37dBm (approx) 0.5W = 27 dBm 0.05W = 17 dBm 0.005W = 7 dBm 0.0005W = -3 dBm 0.00005W = -13 dBm 0.000005W = -23 dBm, ie 60dB attenuation this is in the measurement range. You don't have to purchase? 60dB attenuator, could have at least a 5W 30dB & a 1W 30dB, together giving 60dB. Or any combination adding up to 60dB. Be aware there is a small loss through the connectors & I would use at least a 10W attenuator at the start. On Wed, 13 Nov 2024, 5:27?am W0LEV via , <davearea51a=[email protected]> wrote:
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Re: Why transmitter power attenuator for TinySA?
Most filters present quite a complex load impedance when used out-of-band.? The filters may or may not influence the levels of harmonics or spurs indicated on the SA. Dave - W?LEV On Wed, Nov 13, 2024 at 7:40?PM Toni Ciscar via <aciscar=[email protected]> wrote:
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Dave - W?LEV |
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Re: Why transmitter power attenuator for TinySA?
As John Cunliffe said in this forum (/g/tinysa/message/9655), when measuring harmonics, you can use well defined high pass filters that suppresses the fundamental, for exemple, by >50db . This permits the measurement of harmonics that are very small without overloading the front end. You do only add 50 dBc to your meausurements. |
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Re: Why transmitter power attenuator for TinySA?
Well if you want to measure spurious outputs from a transmitter the Tiny Sa can do that easily, but you must use an attenuation to keep the levels within the allowable limits. Some take the harmonics measurement with an appropriate attenuation, then add an additional attenuation and take the readings. In some cases the input of the Sa can be overloaded and it produces harmonics. By running the test that way you can be sure the trash is coming from the transmitter. You can use the Sa to verify compliance with FCC. Quite a few of the lower cost it's don't meet the spec. The Tiny Sa Ultra has a harmonics mode. On Wed, Nov 13, 2024, 7:54?AM Fred Murray via <fredmurray919=[email protected]> wrote:
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Re: Why transmitter power attenuator for TinySA?
One of the primary uses of a spectrum analyser is to do various measurements on a transmitter; such as harmonic levels and spectral purity.Maybe I misunderstand why anyone might want to connect the output port of an active transmitter to any port of a TinySA. These cannot be done accurately without a direct connection, albeit via attenuation of the required amount. 73 Jeff G8HUL |
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Why transmitter power attenuator for TinySA?
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Never stellar, my aging mind deteriorates faster than I am aware of.
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I do understand why I should use an attenuator to protect various pieces of equipment from "excessive" rf.
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Maybe I misunderstand why anyone might want to connect the output port of an active transmitter to any port of a TinySA.
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Regarding the hf rf environment of my home, I have found a tv high pass filter to be of value for my sdr setup and TinySA use; in particular:
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https://www.amazon.com/Channel-Master-CM-3250-Removes-Interference/dp/B09D45W9TZ?crid=3PQAOWQS31FYB&dib=eyJ2IjoiMSJ9.Y2HOVCF212tTm66x7HgnXa_eg9UziRcmHiv4nRmMz-cphvGuVv1LsMv9aR946XSRSs8mKUIKrCYFaCV13vC3mGM3YzJCLuYxq7pq_yZUD0Mb9aACEIskW3BuKPi6QpfF8BxYxfxfb85OY9Clbm1vsg-WEN12SwtHlTdm3Z_x2GdgwZ5MfyiDnJK3ZnnSFaYS0vZ08vq4uf7s-qyqC1zhnGzKiLxcTiASf0SRdcIaxiU.KInQcucr-cRdaJSNTZKgFMmAScUyxz5b1bhZrJ6rzTw&dib_tag=se&keywords=high+pass+filter&qid=1731501343&sprefix=channel+master+high+pass+filter%2Caps%2C191&sr=8-1
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Too much to learn and not enough mind or time.
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wa4hei
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Re: Setup FM mobile VHF transceiver's deviation with VaraFM
Does anyone read the specifications?? Or they may read them but have absolutely no understanding of what they entail.? Yes, for faithful representation of the input, -25 dBm is specified. ? In an attempt to keep things simple, every 10 dB is equivalent to multiplying by 0.1, or move the decimal point one place to the left. 5-watts: ? add 10 dB attenuator ?? end with 0.5 watts? 5-watts ?? add another 10 dB attenuator for a total of 20 dB ? end with 0.05 watts 5-watts ?? add another 10 dB attenuator for a total of 30 dB ? end with 0.005 watts 5-watts ?? add another 10 dB attenuator for a total of 40 dB ? end with 0.0005 watts 5-watts??? add another 10 dB attenuator for a total of 50 dB?? end with 0.00005 watts We all (should have) learned base 10 arithmetic in grade school.? Logarithms in Jr. HS or beginning HS.?? Dave - W?LEV On Tue, Nov 12, 2024 at 9:29?AM G8HUL via <g8hul=[email protected]> wrote: Also be aware that even at -10dBm, which is well below the damage level, the TinySA may still be slightly overloaded and not give accurate results on some measurements. At least 60db of attenuation would be required for a 5W input. --
Dave - W?LEV |
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Re: Setup FM mobile VHF transceiver's deviation with VaraFM
I'd agree with Bruce, just observe the occupied bandwidth of your transmission, using a suitably narrow RBW setting.
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It will be close enough to the desired value.
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Regards,
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Martin
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On Mon, Nov 11, 2024 at 11:27 PM, Bruce Akhurst wrote:
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Re: Setup FM mobile VHF transceiver's deviation with VaraFM
I am not sure if you can do the measurement with the VaraFM modem, the frequency of the tone has to be at the frequency that is required to get a null in the spectrum for the desired deviation.
In other words you have to calculate the frequency of the tone to match the deviation that you require. 73 Jeff G8HUL |
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Re: Setup FM mobile VHF transceiver's deviation with VaraFM
Also be aware that even at -10dBm, which is well below the damage level, the TinySA may still be slightly overloaded and not give accurate results on some measurements. At least 60db of attenuation would be required for a 5W input.
An input of -25dBm or less is recommended. 73 Jeff G8HUL ________________________________________ From: [email protected] <[email protected]> on behalf of Gary W9TD via groups.io <w9td@...> Sent: 11 November 2024 18:43 To: [email protected] Subject: Re: [tinysa] Setup FM mobile VHF transceiver's deviation with VaraFM Todd, You need 50 dB of external attenuation to keep the level at the Ultra at -10dBm or less. You also might be able to use the supplied antenna with your radio feeding a dummy load. You cannot use the VARA modem as it will not create a single frequency tone, you need an external audio source like Audigy on your computer to generate a tone and send it through the USB to the DRA-50. Gary W9TD |
Ismo V??n?nen OH2FTG
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